Package org.apache.commons.rng.core.source64

Class L64X256Mix

java.lang.Object

org.apache.commons.rng.core.BaseProvider

org.apache.commons.rng.core.source64.LongProvider

org.apache.commons.rng.core.source64.L64X256Mix

All Implemented Interfaces:

RandomLongSource, JumpableUniformRandomProvider, LongJumpableUniformRandomProvider, RestorableUniformRandomProvider, SplittableUniformRandomProvider, UniformRandomProvider

public class L64X256Mix
extends LongProvider
implements SplittableUniformRandomProvider

A 64-bit all purpose generator.

This is a member of the LXM family of generators: L=Linear congruential generator; X=Xor based generator; and M=Mix. This member uses a 64-bit LCG and 256-bit Xor-based generator. It is named as "L64X256MixRandom" in the java.util.random package introduced in JDK 17; the LXM family is described in further detail in:

Steele and Vigna (2021) LXM: better splittable pseudorandom number generators (and almost as fast). Proceedings of the ACM on Programming Languages, Volume 5, Article 148, pp 1–31.

Memory footprint is 384 bits and the period is 2⁶⁴ (2²⁵⁶ - 1).

This generator implements LongJumpableUniformRandomProvider. In addition instances created with a different additive parameter for the LCG are robust against accidental correlation in a multi-threaded setting. The additive parameters must be different in the most significant 63-bits.

This generator implements SplittableUniformRandomProvider. The stream of generators created using the splits methods support parallelisation and are robust against accidental correlation by using unique values for the additive parameter for each instance in the same stream. The primitive streaming methods support parallelisation but with no assurances of accidental correlation; each thread uses a new instance with a randomly initialised state.

Since:

1.5

See Also:

Steele & Vigna (2021) Proc. ACM Programming Languages 5, 1-31, JDK 17 java.util.random javadoc

Field Summary

Fields

Modifier and Type	Field	Description
protected long	la	Per-instance LCG additive parameter (must be odd).
protected long	ls	State of the LCG generator.

Constructor Summary

Constructors

Modifier	Constructor	Description
	L64X256Mix(long[] seed)	Creates a new instance.
	L64X256Mix(long seed0, long seed1, long seed2, long seed3, long seed4, long seed5)	Creates a new instance using a 6 element seed.
protected	L64X256Mix(L64X256Mix source)	Creates a copy instance.

Method Summary

Modifier and Type	Method	Description
protected byte[]	getStateInternal()	Creates a snapshot of the RNG state.
UniformRandomProvider	jump()	Creates a copy of the UniformRandomProvider and then retreats the state of the current instance.
JumpableUniformRandomProvider	longJump()	Creates a copy of the UniformRandomProvider and then retreats the state of the current instance.
long	next()
protected void	setStateInternal(byte[] s)	Resets the RNG to the given state.
SplittableUniformRandomProvider	split(UniformRandomProvider source)
Stream<SplittableUniformRandomProvider>	splits(long streamSize, SplittableUniformRandomProvider source)

Methods inherited from class org.apache.commons.rng.core.source64.LongProvider

nextBoolean, nextInt, nextLong, resetCachedState

Methods inherited from class org.apache.commons.rng.core.BaseProvider

checkIndex, checkStateSize, composeStateInternal, extendSeed, extendSeed, fillState, fillState, restoreState, saveState, splitStateInternal, toString

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface org.apache.commons.rng.JumpableUniformRandomProvider

jumps, jumps

Methods inherited from interface org.apache.commons.rng.LongJumpableUniformRandomProvider

longJumps, longJumps

Methods inherited from interface org.apache.commons.rng.SplittableUniformRandomProvider

doubles, doubles, doubles, doubles, ints, ints, ints, ints, longs, longs, longs, longs, split, splits, splits, splits

Methods inherited from interface org.apache.commons.rng.UniformRandomProvider

nextBoolean, nextBytes, nextBytes, nextDouble, nextDouble, nextDouble, nextFloat, nextFloat, nextFloat, nextInt, nextInt, nextInt, nextLong, nextLong, nextLong

Field Detail

la

protected long la

Per-instance LCG additive parameter (must be odd). Cannot be final to support RestorableUniformRandomProvider.

ls

protected long ls

State of the LCG generator.

Constructor Detail

L64X256Mix

public L64X256Mix(long[] seed)

Creates a new instance.

Parameters:

seed - Initial seed. If the length is larger than 6, only the first 6 elements will be used; if smaller, the remaining elements will be automatically set. A seed containing all zeros in the last four elements will create a non-functional XBG sub-generator and a low quality output with a period of 2⁶⁴.

The 1st element is used to set the LCG increment; the least significant bit is set to odd to ensure a full period LCG. The 2nd element is used to set the LCG state.

L64X256Mix

public L64X256Mix(long seed0,
                  long seed1,
                  long seed2,
                  long seed3,
                  long seed4,
                  long seed5)

Creates a new instance using a 6 element seed. A seed containing all zeros in the last four elements will create a non-functional XBG sub-generator and a low quality output with a period of 2⁶⁴.

The 1st element is used to set the LCG increment; the least significant bit is set to odd to ensure a full period LCG. The 2nd element is used to set the LCG state.

Parameters:

seed0 - Initial seed element 0.

seed1 - Initial seed element 1.

seed2 - Initial seed element 2.

seed3 - Initial seed element 3.

seed4 - Initial seed element 4.

seed5 - Initial seed element 5.

L64X256Mix

protected L64X256Mix(L64X256Mix source)

Creates a copy instance.

Parameters:

source - Source to copy.

Method Detail

getStateInternal

protected byte[] getStateInternal()

Creates a snapshot of the RNG state.

Returns:

the internal state.

setStateInternal

protected void setStateInternal(byte[] s)

Resets the RNG to the given state.

Parameters:

s - State (previously obtained by a call to BaseProvider.getStateInternal()).

See Also:

BaseProvider.checkStateSize(byte[],int)

next

public long next()

Specified by:

next in interface RandomLongSource

Returns:

the next random value.

jump

public UniformRandomProvider jump()

Creates a copy of the UniformRandomProvider and then retreats the state of the current instance. The copy is returned.

The jump is performed by advancing the state of the LCG sub-generator by 1 cycle. The XBG state is unchanged.

The jump size is the equivalent of moving the state backwards by (2²⁵⁶ - 1) positions. It can provide up to 2⁶⁴ non-overlapping subsequences.

Specified by:

jump in interface JumpableUniformRandomProvider

longJump

public JumpableUniformRandomProvider longJump()

Creates a copy of the UniformRandomProvider and then retreats the state of the current instance. The copy is returned.

The jump is performed by advancing the state of the LCG sub-generator by 2³² cycles. The XBG state is unchanged.

The jump size is the equivalent of moving the state backwards by 2³² (2²⁵⁶ - 1) positions. It can provide up to 2³² non-overlapping subsequences of length 2³² (2²⁵⁶ - 1); each subsequence can provide up to 2³² non-overlapping subsequences of length (2²⁵⁶ - 1) using the jump() method.

Specified by:

longJump in interface LongJumpableUniformRandomProvider

split

public SplittableUniformRandomProvider split(UniformRandomProvider source)

Specified by:

split in interface SplittableUniformRandomProvider

splits

public Stream<SplittableUniformRandomProvider> splits(long streamSize,
                                                      SplittableUniformRandomProvider source)

Specified by:

splits in interface SplittableUniformRandomProvider